Glossary of game theory terms.

Mutual Knowledge

Something in a game is Mutual Knowledge if all players know it.
A seemingly simple concept, mutual knowledge is insufficient to analyze most games, since it is not clear from this assumption alone
what people think others know. I might know that X is true, but my actions may depend on whether or not other players know that I know X.
A common additional assumption is that the facts of the game are not only mutual knowledge but also common knowledge. This implies that
we all know X, and we all know that everyone else knows X, and we all know that everyone knows that everyone else knows X, and so on.